Wireless sensor networks have advantage over wired connection because the cost of running wire for a sensor can be as high as 50% to 90% of the cost of the sensor. Thus, substantial advantage can be achieved by using integrated wireless sensing solutions, such as G-Link, which includes wireless accelerometers, SG-Link, which includes wireless strain gauges, and TC Link, which includes wireless thermocouples, all available from MicroStrain, Inc. Williston, Vt. These systems include surface acoustic wave (SAW) resonator RF links as well as wireless transceiver chipsets to produce low power, high speed datalogging transceiver systems with integrated signal conditioning and integrated micro-electromechanical systems (MEMS) sensors. However, since these RF communications systems operate on a narrowband frequency, several of them have not been able to communicate simultaneously without interfering with each other. MicroStrain overcame this problem by storing data locally in addressable dataloggers, which can be commanded by the host base station to simultaneously log data to local memory, as described in issued/copending U.S. patent applications Ser. Nos. 09/731,066, and 10/379,224, incorporated herein by reference. In that scheme, each of the systems can be polled sequentially and their stored data downloaded individually to a base station including a personal computer.
However, substantial delay is introduced in the base station receiving the information by this datalogging and later transmission scheme. In some applications wireless sensors can stream data continuously to a base station over a single radio frequency channel. With multiple sensors on the same channel this streaming must be done sequentially, which makes synchronization of data from these sensors more difficult. Since many applications require that data from multiple sensors be received and analyzed in real time, so that data from various sensors can be correlated, a network of wired sensors that intrinsically provide this capability has been preferred.
A network of wired sensors have also been preferred because many sensor data analysis systems in current use are designed for input with analog voltages as obtained from wires directly connected to the sensors. Wireless networks, such as G-Link (TM Microstrain, Inc., Williston, Vt.), SG Link (TM Microstrain, Inc., Williston, Vt.), and TC Link (TM Microstrain, Inc., Williston, Vt.) have converted data from analog to digital at each sensor location and then transmitted the digital data to a base station.
Many analysis systems have used analog voltage inputs and thus there has been a need for base stations to provide analog output while preserving digital wireless communications from sensors to base station. Thus, a better system is needed that can provide continuous real time sensor data transmission by a plurality of sensor systems in a network and that can provide all this sensor data for input to sensor data analysis systems in analog form while preserving the advantages of digital communication which allows for detection of communication errors and which is inherently robust, and this solution is provided by the following invention.